Magnetic storage drives typically use magneto-resistive heads (also know as MR heads, MR sensors and MR elements) to read data from and write data to magnetic storage disks. MR heads exhibit a high sensitivity to damage caused by voltages arising through the process of electrostatic induction (ESI). ESI induces an electric field from one object to create and electric charge or voltage on a second, nearby object. This occurs by virtue of the first object's changing electric field changing the charge distribution on the second object. Frequently, this occurs in the absence of physical contact between the two objects.
An ESI voltage may arise, for example, on a spinning object, such as a magnetic storage disk, even in the absence of any object physically contacting the disk. Due to inherent capacitance between the spinning disk and the MR head, the ESI voltage may cause a breakdown voltage spike to occur between the MR head and the associated disk. Such a voltage spike may damage the MR head and cause hard drive failure.
One method that has been used in older drives to address the ESI voltage problem uses a silver-graphite ground button that contacts the spinning disk shaft. The silver-graphite ground button, by contacting the spinning disk, provides a ground path from the disk to the hard drive base. Unfortunately, this approach adds undesirable friction and vibration to hard drive operation. Hard drive magnetic storage disk rotational rates are presently extending beyond 7200 rpm to 15,000 and higher. At these rotational rates, such friction and vibration become increasingly unacceptable.
Another approach for solving the ESI voltage problem may use the bearing between the disk drive and the disk as conductive path to ground. Ideally, the bearing could provide a discharge path for the ESI voltage. Here, the unfortunate fact of most such bearings, such as the popular fluid dynamic bearing (FDB), air bearing, or needle bearing, demonstrate poor conductive properties. For example, resistance measurements between the spinning magnetic storage disk and base plate with and FDB may be between 1 MΩ and 400 MΩ. As a result, only a tribocharging current of only 10−9 A can exist to discharge a generated ESI voltage. Consequently, a 4V or more ESI voltage may arise on the disk. Such a charge can result in breakdown voltage spikes and associated destructive high current and temperature levels arising between the MR head and the disk.
Accordingly, there is a need to avoid or reduce the adverse effects of a generated ESI voltage arising on a rapidly rotating object, such as a magnetic storage disk within a hard drive. Such a method and system, for example, would prevent the damage arising from voltage breakdown between the disk and MR head.
A need exists for a method and system for avoiding or reducing the adverse effects such an ESI voltage on a rapidly rotating object, such a magnetic storage disk, which does not introduce unwanted friction or vibration into the objects operation.
A further need exists for a method and system for avoiding such ESI voltage buildup and the associated MR head and disk damage, which also does not rely on conduction through a high impedance path to ground such as an FDB.
Still further, there is the general need for a solution to the problem of ESI voltage arising on a rapidly spinning disk or other object which also does not increase either the manufacturing or operating costs of the hard drive or other device employing the spinning disk or other object.